1. Technical Field
The present invention relates to a method and a system for monitoring moisture in powdered material used to create nuclear fuel. More specifically, the present invention relates to in-line moisture detection for determining the moisture content of uranium-containing powders, including uranium dioxide powder.
2. Background Art
The moisture content of powders used to create nuclear fuels must be monitored closely. For example, for moderation control, the moisture content of uranium dioxide powder must not exceed 1.0% by weight to avoid any possibility of a criticality accident as required by the United States Nuclear Regulatory Commission.
The current method for measuring moisture content of uranium dioxide powders requires removal of a sample from in-process powder. The sample is then analyzed using known techniques such as hydrolysis and hot extraction (total H.sub.2).
While current methods for measuring the moisture content of the powder sample have resulted in accurate sample measurements, the sample moisture content is not always representative of the moisture of the entire in-process powder. For example, the sample may contain more or less moisture then the powder from which it was taken. In the event that the sample contains more moisture, unnecessary delays in future processing steps may result because the powder, based upon the results of the sample test, will be subjected to unnecessary additional drying procedures. In the event that the sample contains less moisture than is the case, powder having too much moisture may be passed on for future processing, leading to difficulties at later fuel processing stages.
Moreover, the method currently used requires that a sample be removed from the in-process powder and separately analyzed. Not only does such a method require additional time for removal, preparation and analysis of the sample, but handling of the sample to avoid contamination increases the cost relating to the powder processing. Furthermore, while the sample is taken, prepared and analyzed, the remaining powder remains idle until a moisture reading on the sample is received. The time required for removal, preparation and analysis of a sampling is approximately two to six hours. Accordingly, the in-process uranium dioxide powder remains idle for a significant period of time while the moisture content of the sample is measured. This time period is multiplied each time the sample fails to meet the moisture requirements because additional samples and testing must occur to verify that the powder is ready for further processing after additional steps are taken to remove the moisture in the powder.
Numerous attempts have been made in the past to develop a technique for rapid or in-process determination of moisture in uranium dioxide powder so as to avoid the sampling method currently in use. These efforts involved direct powder moisture measurement or indirect measurement of the atmosphere around the powder. In each case, the measurement process or configuration was not adequately sensitive or stable in the powder moisture range of 0-1.0 wt %.
It is desirable to develop an accurate, reliable and stable measure of the overall moisture content of a nuclear fuel powder, such as uranium dioxide, particularly when the moisture content is in the range of 0-1.0% by weight.